This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Metals and metalloproteins are essential for many cellular processes. Our laboratory uses macromolecular X-ray crystallography to study the structure and function of metalloproteins. These proteins include nickel regulatory transcription factor NikR, a DNA-binding protein that regulates cellular nickel uptake;the radical S-adenosylmethionine (SAM) enzymes biotin synthase (BioB), involved in biotin biosynthesis, and pyruvate formate-lyase (PFL) activating enzyme (PflAE), involved in anaerobic metabolism by formation of a protein bound glycyl radical on PFL;and hydroxypropylphosphonic acid epoxidase (HppE), which uses a mononuclear iron site to catalyze a unique epoxidation in the formation of the antibiotic fosfomycin. We have solved and published initial crystal structures of all of these proteins, and some of this work was carried out previously at SSRL. We are now in pursuit of further crystallographic characterization of these metalloenzymes in multiple states to more fully understand their functional properties.